The invention relates to a magnetic material in which the main phase is formed by an intermetallic compound of the rare earth transition metal type.
Magnetic materials based on intermetallic compounds of certain rare earth metals with transition metals (RE-TM) may be formed into permanent magnets having coercive forces of considerable magnitude (several kOe). The magnetic materials in question are for this purpose ground to particles having a subcrystalline size and then aligned in a magnetic field. The alignment of the particles and hence the magnetic orientation is then fixed by sintering or by immersing the particles in a (synthetic material) binder or in a low-melting-point metal such as lead. These methods are referred to as powder-metallurgic methods of manufacturing rare earth metal-transition metal magnets. In such a treatment these intermetallic compounds develop unusually high intrinsic coercive forces at room temperature.
The most commonly known intermetallic compounds which can be processed into magnets by powder metallurgy contain essentially quantities of samarium and cobalt, for example, single-phase SmCo.sub.5 and multiphase SmCo.sub.z in which z.apprxeq.7. Item 1. Permanent magnets based on single-phase SmCo.sub.5 are currently produced in large quantities. The energy products are of the order of 20 MG Oe. Permanent magnets based on multiphase SmCo.sub.z in which z.apprxeq.7 and in which Co is partly replaced by Fe and Cu have higher energy products (27 MG Oe). Preparation of this class of magnets is, however, extremely difficult and complicated.
The most recently devised types of rare earth transition metal magnets are based on ternary compounds of the type R.sub.2 Fe.sub.14 B (R=Nd, Pr), which have still higher energy products of approximately 35 Mg Oe. The preparation of these magnets can be compared with that described under item 1, that is to say, the preparation is simpler than that of multiphase SmCo.sub.z magnets described under item 2. A drawback of the R.sub.2 Fe.sub.14 B magnet is the low Curie temperature (T.sub.c =307.degree. C.) and the attendant high negative temperature coefficient of the magnetization .sigma. and of the coercive force H.sub.c. This drawback may be partly removed by Co substitution. This has been described in EP-A 106,948.
However, the above-mentioned publication states that when substituting Fe by Co, the coercive force starts to decrease from the situation in which 25% of Fe is substituted by Co and that not more than 50% of Fe should be substituted by Co in order to produce a material having a coercive force of 80 kA/m or more, which is that required for a magnet to be of use in practice. Consequently, the advantage of the rise in Curie temperature by substitution of Co is usable only to a limited extent.